This composite image of the Whirlpool Galaxy, Messier 51, shows that the radio emission from the galaxy’s cold hydrogen gas (blue) extends well beyond the optical light emitted by its stars (Credit: NRAO/AUI, J. Uson).

Radio astronomy is the study of the invisible universe

We see the world around us because our eyes detect visible light, a type of electromagnetic radiation. Objects on Earth and in space also emit other types of electromagnetic radiation that cannot be seen by the human eye, such as radio waves. The full range of radiation emitted by an object is called its electromagnetic spectrum.

Radio astronomy is the study of celestial objects that emit radio waves. With radio astronomy, scientists can study astronomical phenomena that are often invisible in other portions of the electromagnetic spectrum.

Using radio astronomy techniques, astronomers can observe the Cosmic Microwave Background Radiation, which is the remnant signal of the birth of our Universe in the Big Bang. They can also probe the “Dark Ages” before the onset of the first stars or galaxies, and study the earliest generation of galaxies. Radio astronomers analyze and explore the black holes that live at the hearts of most galaxies.
Since radio waves penetrate dust, scientists use radio astronomy techniques to study regions that cannot be seen in visible light, such as the dust-shrouded environments where stars and planets are born, and the center of our Galaxy, the Milky Way. Radio waves also allow astronomers to trace the location, density, and motion of the hydrogen gas that constitutes three-fourths of the ordinary matter in the Universe.